The present invention relates to a parallelogram bracket which has a pair of rod members pivotally connected to end members and has a force balancing mechanism which utilizes a pneumatic spring situated in the parallelogram bracket. A piston of the pneumatic spring is supported against parts which are connected to one of the articulated axles and the piston rod is supported against parts of the parallelogram rod member connected to the other articulated axle situated diagonally opposite thereto.
A known parallelogram bracket, which is disclosed in U.S. Pat. No. 4,166,602, is provided for holding an x-ray unit and has a pneumatic spring which is situated in a hollow cast member forming one of the arm members of the parallelogram. The pneumatic spring includes a cylinder containing a piston which is connected to a piston rod which cylinder and piston rod are each provided with an end piece of which one is linked to a yoke applied to the cast member and the other is linked to a lug interacting with an adjustment screw. The point of attachment for the piston rod can be changed with the adjustment screw and thus the moment of force can be modified and thus adapted to loads of different weights. The end pieces are connected to the piston rod and respectively to the cylinder by means of screw-type connections so that the ends of the cylinder and piston rods must be mated to the end pieces and thus the structure of the parallelogram bracket.
Even though the mechanical outlay can be clearly reduced in comparison to traditional bracket structures working with compression springs, chains and cam elements by employing a pneumatic spring, the known bracket structure is nonetheless relatively complicated particularly in view of the assembly and disassembly of the pneumatic spring as well as the use of the bracket for carrying other objects with loads of different weights lying outside of the range of the adjustment of the adjusting screw. To compensate for loads having a weight outside of the range for the bracket structure, the structure must be disassembled because the range of weight compensation for loads of this structure is essentially a relatively narrow range.